This invention relates to radio receivers and more specifically to scan operations used in radio receivers.
Scanning is a technique by which many communication receiver devices detect and lock on a frequency channel when qualified signal activity is present on that channel. In most two-way radios or other FM tuners that have scan capability, each individual channel frequency in a scan list is scanned in search of channel activity in increasing order until the last frequency in the scan list is reached. The scanning then continues from the beginning of the list. In this typical scanning technique, a voltage controlled oscillator (VCO) within a phase lock loop (PLL) tunes to each frequency/channel in the scan list, one channel at a time, so that channel activity detection can be performed. The scan operation stops on a channel whenever a qualified signal (i.e. channel activity) is detected on that channel.
One of the significant limitations with existing scan techniques is the time delay required for the VCO/PLL to lock on each frequency in the scan list. The VCO/PLL lock time is typically the most significant time delay of the scanning function. Lock times for each channel on the order of 10 milliseconds (ms) are common, not including the signal detection time or channel activity search time.
The entire scan list for a typical radio receiver usually covers many channels over several megahertz of frequency range. A large frequency scan list contributes to communication problems including missed calls, missed channel activity detections, as well as delays in establishing a communications link. Missed calls, delays, and link failures are sources of annoyance and inconvenience for the user.
Accordingly, an improved scanning technique that minimizes delays would be beneficial in today""s communication""s environment.